NMDA-Type Glutamate Receptor Activation Promotes Vascular Remodeling and Pulmonary Arterial Hypertension

Background —Excessive proliferation and apoptosis resistance in pulmonary vascular cells underlie vascular remodeling in pulmonary arterial hypertension (PAH). Specific treatments for PAH exist, mostly targeting endothelial dysfunction, but high pulmonary arterial pressure still causes heart failure and death. Pulmonary vascular remodeling may be driven by metabolic reprogramming of vascular cells to increase glutaminolysis and glutamate production. The N-methyl-D-aspartate receptor (NMDAR), a major neuronal glutamate receptor, is also expressed on vascular cells, but its role in PAH is unknown. Methods —We assessed the status of the glutamate-NMDAR axis in the pulmonary arteries of PAH patients and controls, through mass spectrometry imaging, western blotting and immunohistochemistry. We measured the glutamate release from cultured pulmonary vascular cells using enzymatic assays, and analyzed NMDAR regulation/phosphorylation through western blot experiments. The effect of NMDAR blockade on human pulmonary arterial smooth muscle cell (hPASMC) proliferation was determined using a BrdU incorporation assay. We assessed the role of NMDARs in vascular remodeling associated to pulmonary hypertension (PH), both in smooth muscle-specific NMDAR knockout mice exposed to chronic hypoxia and in the monocrotaline rat model of PH using NMDAR blockers. Results —We report glutamate accumulation, upregulation of the NMDAR, and NMDAR engagement reflected by increases in GluN1-subunit phosphorylation, in the pulmonary arteries of human PAH patients. K v channel inhibition and ETAR activation amplified calcium-dependent glutamate release from hPASMCs, and ETAR and PDGFR activation led to NMDAR engagement, highlighting crosstalk between the glutamate-NMDAR axis and major PAH-associated pathways. The PDGF-BB-induced proliferation of hPASMCs involved NMDAR activation and phosphorylated GluN1 subunit localization to cell-cell contacts, consistent with glutamatergic communication between proliferating hPASMCs via NMDARs. Smooth-muscle NMDAR deficiency in mice attenuated the vascular remodeling triggered by chronic hypoxia, highlighting the role of vascular NMDARs in PH. Pharmacological NMDAR blockade in the monocrotaline rat model of PH had beneficial effects on cardiac and vascular remodeling, decreasing endothelial dysfunction, cell proliferation and apoptosis resistance, while disrupting the glutamate-NMDAR pathway in pulmonary arteries. Conclusions —These results reveal a dysregulation of the glutamate-NMDAR axis in the pulmonary arteries of PAH patients, and identify vascular NMDARs as targets for anti-remodeling treatments in PAH.